Upright vacuum cleaners are designed primarily for cleaning rugs and carpets, and generally include a rotatable brush housed in a suction chamber in a floor nozzle for scraping up and drawing in dust particles from deep inside the pile. Although the upright vacuum cleaners are useful for cleaning the rugs and carpets, they are not suitable for thorough cleaning of uncarpeted floors since the rotatable brush tends to damage the floor as well as cause dust to fly away from the brush on the floor.
Devices are known to eliminate the above problems.
One such devices includes a V belt extending under tension between the shaft of a motor and the pulley of a rotatable brush, the pulley having a V-shaped groove variable in width for receiving the V belt. When the width of the V-shaped groove is reduced, the force with which the V belt is pressed against the surface of the groove is increased to the point where rotative power is transmitted from the motor to the rotatable brush. Conversely, when the groove width is increased, the V belt slips in the groove to prevent the brush from rotating. This prior art device requires a complicated mechanism for adjusting the groove width in the pulley, and further requires an intermediate pulley for constantly tensioning the V belt, resulting in an increased cost of the vacuum cleaner. The proposed attempt is particularly disadvantageous in that, when the rotatable brush is at rest, the V belt slips in the pulley groove and becomes much less durable due to heat generated by friction between the V belt and the groove surface.
According to another proposed expedient, the pulley around which a belt is looped is operatively coupled to the rotatable brush through a magnetic clutch. The rotatable brush, however, cannot be completely stopped due to the influence of magnetic flux even when the magnetic clutch is disconnected. To cope with this problem, a special brake mechanism is required to brake the rotary brush, an arrangement which makes the vacuum cleaner disadvantageous from the standpoint of construction and cost of manufacture.